Transmission control with electronic governor and trim boost

ABSTRACT

A transmission control has a redundancy control for upshift and downshift control of friction torque transmitting devices in a power transmission. The control solenoid valves providing for continued governor and accumulator trim boost in the event of a malfunction, in either the electrical system or the hydraulic system, which affects the governor pressure schedule. A reverse control signal, from a manual valve, is effective to remove the malfunctioning solenoid valve from effective operation in the control.

TECHNICAL FIELD

The present invention relates generally to transmission controls. Moreparticularly, the present invention relates to transmission controlshaving electrical and hydraulic controls. Specifically, the presentinvention relates to transmission control valving wherein multipleaccumulators have a trim pressure supplied by a single regulator valveand shift control signals that are continued in the event of amalfunction.

BACKGROUND OF THE INVENTION

Power-shifting automatic transmissions of both the planetary type andcountershaft type use hydraulically actuated, friction torque devices toeffect the selection of sequential drive ranges. Planetary typetransmissions use friction torque transfer devices of both the clutchand brake variety. Countershaft type transmissions use friction torquetransfer devices of only the clutch variety. The control mechanism whichdetermines the shift sequence and timing for these transmissions can beeither hydraulic control valving or the more recently introducedelectro-hydraulic control valving. With electro-hydraulic controls, apre-programmed digital computer is generally provided to determine boththe shift schedules and pressure levels of the hydraulic actuating fluidwithin the transmission. The computer employs a look-up table which hasthe necessary data to determine the shift points in response to inputsignals from vehicle parameter detectors such as the vehicle and enginespeed sensors, engine torque level sensors, throttle position sensors,and the like.

The computer analyzes the input signals and refers to the look-up tableto determine the appropriate ratio interchange. The computer can alsoprovide the necessary control signals to establish the output pressureof the solenoid valve. Generally the solenoid valves are either of theoff-on type or the pulse width modulated (PWM) type. With either type,the output signal is delivered to either a valve, which will control theratio interchange, or to the friction devices directly.

The control devices currently known have a governor and throttle signalto control the ratio interchange. In some instances this signal iscombined by the electronics to provide a single electrical output signalwhich will determine the output pressure of the solenoid controlvalving. Should the solenoid have a malfunction, the transmissioncontrol includes a limp-home feature which causes the transmission toselect a fixed gear ratio until proper repairs are undertaken. Thisfeature prevents the driver from being stranded due to an electric ormechanical malfunction of the solenoids.

SUMMARY OF THE INVENTION

It is, therefore, a primary object of the present invention to providean improved transmission control having full redundancy to permitcontinued full feature operation in the event of a solenoid or valvemalfunction.

It is another object of the present invention to provide an improvedtransmission control, as above, wherein a driver alert to a single pointmalfunction is signalled by harsh shifts which result from increasedtrim boost pressure.

It is a further object of the present invention to provide an improvedtransmission control, as above, wherein an electronic governor and trimvalve provide operation in a fifth range under some malfunction modeconditions in order to prevent transmission overspeed.

It is still another object of the present invention to provide animproved transmission control, as above, wherein conventional but harshupshifting and downshifting continues even after the driver comes to astop and selects reverse.

It is yet another object of the present invention to provide an improvedtransmission control, as above, wherein multiple accumulators areprovided with trim pressures from a single regulator valve.

These and other objects of the invention, as well as the advantagesthereof over existing and prior art forms, which will be apparent inview of the following detailed specification, are accomplished by meanshereinafter described and claimed.

The present invention provides full range shifting in the forward ratiosas well as in reverse operation in the event of a malfunction by one ofthe solenoid valves which control a particular ratio interchange in thetransmission.

This control scheme assumes the existence of a cascading hydrauliccontrol circuit that actuate the friction torque transfer devices in anautomatic transmission. Also required are a manual selector valve,trimmer valves or accumulators and fluid operated friction torquetransmitters. This invention consists of four hydraulic control valvesreferred to as:

1. a trim boost valve

2. a governor shuttle valve

3. an "A" solenoid interlock valve

4. a "B" solenoid interlock valve

5. two normally open (N/O) pressure regulating three-way solenoidvalves.

The purpose of the governor shuttle valve is to direct the higher of thetwo solenoid pressures to the governor pressure passage and to the boostside of a plug valve on the trim boost valve. It also directs the lowerof the two solenoid pressures to the other side of the plug on the trimboost valve. Trim boost pressure is maintained at a level determined bya spring which is set by the differential pressure between solenoids "A"and "B" which act on the plug through a pin and stop structure. Duringupshifts, the "B" solenoid is operated at a lower level than the "A"solenoid so that a differential pressure exists on the trim boost plugresulting in the desired trim boost pressure. Between upshifts, the "B"solenoid pressure rises to the same level as the "A" solenoid. The "A"solenoid continues to supply governor pressure. The interlock valveprovides a control that will "lock-out" a solenoid if a malfunctionoccurs that provides a pressure continuously greater than zero. The"lock-out" is introduced when the transmission is shifted to reverse,thereby insuring that the vehicle speed is essentially zero to preventany unscheduled downshifts. The control will permit the operator toresume normal operation although the upshifts will be harsh because ofthe high trim boost. This will remind the operator that some service isneeded.

This hydraulic control scheme allows the control of shifts and trimboost pressure in any transmission control which utilizes cascaded relayvalves and trimmers or accumulators for shift logic when controlling theratio interchange in a transmission. The control provides fullredundancy in the event of a solenoid valve malfunction. During normaloperation, because of the delayed pressure rise in the "B" solenoid, asingle regulator valve provides trim pressure bias for multipleaccumulators

To acquaint persons skilled in the arts most closely related to thepresent invention, one preferred embodiment of a governor controlvalving and a trim valve embodying the concepts of the present inventionand adapted for use with a transmission control, and which illustrates abest mode now contemplated for putting the invention into practice isdescribed herein by, and with reference to, the annexed drawings thatform a part of the specification. The exemplary governor control isdescribed in detail without attempting to show all of the various formsand modification in which the invention might be embodied. As such, theembodiment shown and described herein is illustrative, and as willbecome apparent to those skilled in these arts, can be modified innumerous ways within the spirit and scope of the invention; theinvention being measured by the appended claims and not by the detailsof the specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a transmission and controlembodying the present invention;

FIG. 2A is an enlarged portion of FIG. 1, the outline of which isdelineated by the chain line identified as "FIG. 2A" and depicting arepresentative control valving arrangement incorporating the presentinvention;

FIG. 2B is also an enlarged portion of FIG. 1, the outline of which isdelineated by the chain line identified as "FIG. 2B" and depicting thesource of hydraulic pressure, a pressure regulator assembly, a clutchassembly, the transmission gearing, a cooler and a lube system;

FIG. 2C is also an enlarged portion of FIG. 1, the outline of which isdelineated by the chain line identified as "FIG. 2C" and depicting aselector valve, a forward-reverse control assembly and two of thecascaded shift valves and their related accumulators;

FIG. 2D is also an enlarged portion of FIG. 1, the outline of which isdelineated by the chain line identified as "FIG. 2D" and depicting theremaining two cascaded selector valves and their associatedaccumulators;

FIG. 3 is a graph representing operating parameter values present duringupshifts in transmission control incorporating the present invention;

FIG. 4 is a graph representing operating parameter values present duringdownshifts in a transmission control incorporating the presentinvention;

FIG. 5 is a graph representing typical pressure curves from the solenoidvalves that control the ratio interchanges and trim pressure bias of thetransmission control incorporating the present invention.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT

The overall power transmission and control system embodying the conceptsof the present invention is depicted diagrammatically, and designated bythe numeral 10, in FIG. 1. The gearing portion of the transmission isrepresented at 11 and is preferably constructed in accordance with theteaching of U.S. Pat. No. 5,009,118 issued to Ordo et al on Apr. 23,1991. However, other transmissions can also benefit from the presentinvention. Pressurized hydraulic fluid is provided to the control system13 by a conventional, positive displacement pump 14 which drawshydraulic fluid from a reservoir 15 through a passage 17 for delivery toa main line conduit 18. A conventional pressure regulator 20 controlsthe fluid pressure in the main line conduit 18. The excess fluid--thatis, fluid not needed for transmission control and clutchoperation--delivered by the pump 14 is directed by an overage passage 21to a conventional torque converter and clutch assembly 23. Aconventional exhaust regulator valve 22 limits the fluid pressure at thetorque converter and clutch assembly 23. The fluid flowing from theassembly 23 is directed through a cooler and a lubrication distributionsystem, so designated on FIGS. 1 and 2B of the drawings. The pressure inthe lubrication system circuit is established by a conventionalregulator valve 26.

The main line pressure conduit 18 is connected, by branch 18_(A) with amanual selector valve 24, by branch 18_(B) to a forward-reverse controlassembly 25, by branch 18_(C) to the torque converter and clutchassembly 23, and by branch 18_(D) to a first and second normally openpulse width modulated (PWM) solenoid valves 27 and 28 and an accumulatortrim boost control valve 30. The main line pressure distributed to thetorque converter and clutch assembly 23 is utilized to engage the clutchin a well known manner. The manual selector valve 24 is adapted to bemanipulated in a well known manner to distribute the pressurizedhydraulic fluid in the main line pressure conduit 18 in accordance withthe drive ratio selected by the operator. The selector valve 24 has alongitudinal bore 31 in which a spool valve member 33 is slidablydisposed. The spool valve member 33 has spaced lands 34 and 35 which areadapted to selectively control the flow of main line, pressuredhydraulic fluid from branch 18_(A) of the main line pressure conduit 18to a reverse passage 37 when reverse drive "R" is selected by theoperator and to a forward passage 38 when any forward drive "D1" through"D5" is selected by the operator.

When the operator desires to limit the number of forward drive ratios toless than the maximum number available (five with the depicted control),the manual selector valve 24 can be manipulated to the forward driveconditions "D4" through "D1". In the "D4" condition, main pressure isdistributed to a "D4" passage 40 as well as the forward passage 38. Allof the other passages leading from the selector valve 24 are exhausted.In the "D3" condition, main line pressure is distributed to a "D3"passage 41, as well as the "D4" passage 40 and the forward passage 38.In the "D2" condition, main line pressure is distributed to a "D2"passage 43 as well as the "D3" passage 41, the "D4" passage 40 and theforward passage 38. In the "D1" condition, main pressure is distributedto a "D1" passage 44 as well as the "D2" passage 43, the "D3" passage41, the "D4" passage 40 and the forward passage 38. The effect of thepressure in passages 40, 41, 43 and 44 will be hereinafter discussed ingreater detail.

The forward passage 38 and the reverse passage 37 as well as the mainline pressure conduit 18 are distributed to a forward-reverse controlassembly 25 which is effective to establish the power flow through thetransmission in a well known manner. The above described in theaforesaid Ordo et al patent utilizes a synchronizer to establish theforward or reverse power path. The forward-reverse control assembly 25is preferably constructed in accordance with the assembly described inU.S. patent application, Ser. No. 07/920,744, filed Jun. 1, 1992, in thename of Klemen et al and assigned to the assignee of this application.

The hydraulic control system 13 provides for controlling the engagementand disengagement of the friction torque transfer devices required toestablish the ratios in the transmission 11. The ratio interchangecontrol is provided by four shift valves 47A through 47D, four exhaustvalves 48A through 48D and five accumulators 50A through 50E.

As previewed in the previous paragraph, and as will appear in thedetailed description which follows, a particular structural member,component or arrangement may be employed at more than one location. Whenreferring generally to that type of structural member, component orarrangement a common numerical designation shall be employed. However,when one of the structural members, components or arrangements soidentified is to be individually identified it shall be referenced byvirtue of a letter suffix employed in combination with the numericaldesignation employed for general identification of that structuralmember, component or arrangement. Thus, there are at least four shiftvalves which are generally identified by the numeral 47, but thespecific, individual valves are, therefore, identified as 47A, 47B, 47Cand 47D in the specification and on the drawings. This same suffixconvention shall be employed throughout the specification for othercomponents.

The transmission has five friction torque transfer devices in the natureof clutches designated "C1" through "C5". One of the clutches is engagedfor each drive ratio while the remaining clutches are disengaged. Theclutch "C3" provides both the third forward speed and the reverse speed.A two position shuttle valve 51 is operable to connect the properpassage to the "C3" clutch.

The shift valve 47A controls the one/two ratio interchange and employs aspool valve member 53A having spaced lands 54A, 55A and 57A that areslidably disposed in a bore 58A which communicates with a first clutchfeed passage 60, a first clutch apply passage 61, a second clutch feedpassage 63A, a first clutch exhaust passage 64A, the hydraulic fluidreturn line 65A, the "D1" passage 44 and a governor passage 67. Thespool 53A is biased toward the governor passage 67 by a spring 68A,disposed in a chamber 70, that is located at one end of the bore 58Aadjacent the land 57A. The passage 60 is connected with theforward-reverse control assembly 25 which is effective to distributemain line hydraulic pressure thereto when the forward passage 38 ispressurized.

In the spring set position shown,--that is, when the spool valve membersare disposed solely in response to the biasing action of the spring--thevalve 47A distributes main pressure in the clutch feed passage 60between lands 55A and 57A to the first clutch apply passage 61 to effectengagement of the clutch "C1". The first clutch apply passage 61 is alsoconnected with an accumulator chamber 71A which is a component of theaccumulator 50A. The accumulator 50A also includes a plug 73A, a trimchamber 74A and a spring 75A. The accumulator 50A is effective tocontrol the pressure rise in the clutch "C1" during engagement in a wellknown manner. The trim chamber 74A is pressurized by a controlledpressure in a trim passage 77, which has an effect on the pressure risein the accumulator chamber 71A and therefore the engagement time of theclutch "C1" as represented by the pressure in first clutch apply passage61.

In the pressure set position--that is, the position of the spool valvemembers when the pressure in the governor passage 67 overcomes thespring 68A--the passage 60 is connected between lands 54A and 55A to thesecond clutch feed passage 63A which is in fluid communication with thetwo/three shift valve 47B where it is closed by land 55B on spool valvemember 55B. However, when the spool valve member 53B is in the springset position depicted, an offset passage 78B connects the feed passage63 and the space between lands 55B and 57B to a second clutch applypassage 61B which is effective, when pressurized, to enforce engagementof the second clutch "C2". The engagement time of the second clutch "C2"is affected by the accumulator 50B in the same manner as describedpreviously herein with respect to the accumulator 50A.

The pressure in the second clutch feed passage 63 is also ported toreact with a spool valve member 81A in the exhaust valve 48A. The spoolvalve member 81A includes a pair of spaced lands 83A and 84A. A spring85A biases the spool valve member 81A to one end of a bore 87A in valve48A. The first clutch exhaust passage 64A communicates with the bore 87Athrough a restriction 88A which is connected with an exhaust, orhydraulic fluid return line, 90A. When the shift valve 47A is initiallymoved to the pressure set position, the clutch "C1" will begin toexhaust through the restriction 88A. However, when the pressure inpassage 63A is at a level sufficient to overcome the spring 85A, thespool valve 81A will connect passage 64A directly to the hydraulicreturn line exhaust passage 90A freely to exhaust the clutch "C1". Thetrigger pressure of the exhaust valve 48A is substantially equal to theminimum pressure required for the clutch "C2" to begin transmittingtorque.

As the pressure in the governor passage 67 continues to increase, theshift valves 47C and 47D and will be shifted accordingly to control thesecond/third, third/fourth and fourth/fifth ratio interchanges,respectively. The upshifting occurs in accordance with the clutchinterchange previously explained herein with respect to the first/secondratio interchange. The respective accumulators 50 and exhaust valves 48will control the timing of the interchanges. It should be appreciatedthat the higher ratio clutches cannot be engaged until the next lowerclutch has first been engaged. This is commonly termed a cascadingpressure control. It should also be evident that the shuttle valve 51(FIG. 2D) is effective to connect the passage 61C to the clutch "C3" andthe trim chamber 74C in the accumulator 50C during a two/three ratiointerchange. During downshifting when a clutch is engaged, the higherranking clutches will be disengaged.

If the transmission 10 is in second gear--i.e. the valve 47A hasupshifted, and the pressure in the governor passage 67 is reduced to alevel sufficient to permit the spring 68A to reset (downshift) the shiftvalve 47A to the spring set position, the second clutch "C2" will beexhausted through the hydraulic fluid return line 65A while the clutch"C1" is engaged by pressure in passage 60 being communicated betweenlands 55A and 57A. Rapid disengagement of the off-going clutch, duringdownshifting, is generally preferred to permit the engine to freelyaccelerate to the speed required to accommodate the on-coming ratio.

The reverse ratio is engaged by the manual selector valve 24 beingshifted to the reverse position to pressurize a reverse apply passage 93which is fed through the forward-reverse control 25. When the passage 93is pressurized, the shuttle valve 51 is moved to close the third clutchapply passage 61C from the shift valve 47C and simultaneously connectthe reverse apply passage 93 with the clutch "C3" and the accumulator50C. The reverse apply passage 93 is also connected with first andsecond interlock valves 94 and 95, respectively, which are in fluidcommunication with the respective solenoid valves 27 and 28 for apurpose that will be hereinafter described.

The solenoid valves 27 and 28 are of the modulating type such that eachis capable of establishing a variable pressure output. The pressureoutput of the solenoid valves 27 and 28 will be termed a governorpressure. However, the pressure established by each valve 27 and 28 isaffected by a number of vehicle parameters including vehicle speed andthrottle setting or fuel feed. Other parameters may be provided, asdesired. The signals controlling the PWM solenoid valves 27 and 28 arepreferably established by a conventional pre-programmed digital computerwhich is incorporated in the transmission and control 10 and programmedin a conventional manner to establish the various pressures. Suchcomputers and the operating or control algorithms are well known. Thesolenoid valve 27 is controlled at one pressure schedule while thesolenoid valve 28 is controlled at another pressure schedule duringupshifting. The difference in the schedules permits the solenoid valve27 to operate along the line 97 of the curve shown in FIG. 5 and alsopermits the solenoid valve 28 to operate along the line 98 in that samefigure. As seen in FIG. 5, the pressure output of solenoid valve 27increases before the pressure output of the solenoid valve 28. Thepurpose for these different schedules will be explained in conjunctionwith the description of the valves 30, 94 and 95.

The first interlock valve 94 includes a spool valve member 100 havingspaced lands 101, 103 and 104 slidably disposed in a stepped diameterbore 105. As best seen in FIG. 2A, the second and third lands 103 and104 are of a larger diameter than the first land 101 and cooperate withthe stepped diameter bore 105 to define an interlock chamber 107. Thespool valve member 100 is urged toward one end of the bore 105 by aspring 108 disposed in chamber 110 and compressed between a plug 111 andthe land 104. In the spring set position shown, the output pressure ofsolenoid valve 27 is in fluid communication with the bore 105 betweenthe lands 103 and 104 to provide controlled fluid pressure to a controlpassage 113 which is in fluid communication with a control chamber 114formed on a governor shuttle valve 115. A governor feed passage 117branches from the passage 113 and is also connected with the shuttlevalve 115 between lands 141 and 143 when the spool valve member 136 isdisposed in the position best depicted in FIG. 2A.

The second interlock valve 95 includes a spool valve member 118 havingspaced lands 120, 121 and 123 slidably disposed in a stepped diameterbore 125. As best seen in FIG. 2, the second and third lands 121 and 123are of a larger diameter than the first land 120 and cooperate with thestepped diameter bore 125 to define an interlock chamber 126. The spoolvalve member 118 is urged toward one end of the bore 125 by a spring 127disposed in a chamber 128 and compressed between a plug 130 and the land123. In the spring set position shown, the output pressure of thesolenoid valve 28 is in fluid communication with the bore 125 betweenthe lands 121 and 123 to provide controlled fluid pressure to a controlpassage 131 which is in fluid communication with a control chamber 133formed on the shuttle valve 115. A governor feed passage 134 branchesfrom the passage 131 and is also connected with the shuttle valve 115.

The interlock valves 94 and 95 are both connected with the passage 93which, as previously explained, is pressurized through the manualselecting valve 24 and the forward-reverse control 25 when the reversedrive is selected by the operator. The passage 93 communicates with theface of the lands 101 and 120 to impose a bias pressure thereon wheneverthe reverse drive is selected. In the spring set positions of both spoolvalve members 100 and 118 within the bores 105 and 125, the chambers 107and 126 are in fluid communication with an exhaust, or hydraulic fluidreturn line, 135. The spring chambers 110 and 128 are also in fluidcommunication with an exhaust, or hydraulic fluid return line 137.

When the reverse passage 93 is pressurized, the spool valve members 100and 118 will be moved to a pressure set position. In the pressure setposition the exhaust passage 135 will be closed by the lands 101 and 120from valves 94 and 95, respectively. Also in the pressure set position,the chambers 107 and 126 will be connected with the output pressure ofrespective solenoid valves 27 and 28 and the passages 113 and 131 willbe connected with the exhaust passage 137. During normal operation, thesolenoids 27 and 28 will not provide a pressure output during reverseoperation.

The shuttle valve 115, included a spool valve member 138 having threelands 140, 141 and 143 which are slidably disposed in a bore 144 betweenthe chambers 114, and 133. The bore 144 is disposed in fluidcommunication with the passages 117 and 134 as well as a pair ofgovernor pressure passages 145 and 147, and a secondary trim boostpassage 148. Both governor pressure passages 145 and 147 are connectedwith a primary boost passage 150 which, in turn, communicates with theprimary governor passage 67. The spool valve member 138 in shuttle valve115 is positioned by the pressure in the opposed chambers 114 and 133.It is evident from FIG. 5, that the pressure from solenoid valve 27increases before the pressure from solenoid 28. Therefore, the shuttlevalve 115, during normal forward operation, will be disposed in theposition shown in FIGS. 1 and 2A. So disposed, the pressure fromsolenoid 27 is directed via passages 113, 117 and 145 to the governorpassage 67 and the primary boost passage 150. The passage 147 is closedat the land 140 and the output pressure of the solenoid valve 28 isdirected via passages 31 and 134 to the secondary boost passage 148.

The boost passage 148 is connected for fluid communication with one sideof a boost plug 151, and boost passage 150, through governor passage 67is connected for fluid communication with the opposite side of boostplug 151. The boost plug 151 is a component of the accumulator trimboost valve 30, as depicted in FIG. 2A. The plug 151 cooperates with abore 153 to define a primary chamber 154, connected with governorpassage 67 and thereby indirectly with primary boost passage 150. Asecondary chamber 155 is connected in fluid communication with thesecondary trim boost passage 148. The accumulator trim boost valve 30also includes a regulator valve portion 157 which is connected with theplug 151 through a pin and stop 158, and a spring 160. The regulatorvalve portion 157 includes a valve spool member 161 having spaced lands163 and 164 slidably disposed in a bore 165. The bore 165 is connectedwith the main line pressure conduit branch 18_(D), the trim passage 77and a pair of exhaust, or hydraulic fluid return lines 167. The trimpassage 77 is connected to a control chamber 170 defined between thelands 163 and 164 through a restriction 168.

Fluid pressure in trim passage 77 will urge the spool member 161 againstthe spring 160 in a direction to close the main line pressure conduitbranch 18_(D) at land 163 and open the exhaust passage 167 previouslyclosed by land 164. This action will control the pressure in the trimpassage 77 in a well-known manner. Fluid pressure operating on the plug151 will control the amount of compression in the spring 160 andtherefore, the pressure level at which the regulator valve 157 maintainsthe pressure in trim passage 77. When the plug 151 is urged against thespring 160 by pressure in primary chamber 154, as determined by thesolenoid valve 27, the pressure level in trim passage 77 will be at ahigh level, and when both chambers 154 and 155 are pressurized, thepressure level in trim passage 77 will be at a low level. The pressurelevel in trim passage 77 will provide a bias pressure for the trimchamber 74 in the accumulators 50 (through trim passage 77)--therebyproviding a control pressure for the clutches "C1" through "C5" in awell-known manner.

Operation

With the vehicle engine operating, the pump 14, in conjunction with theregulator 50, provides pressurized hydraulic fluid. With the selectorvalve positioned for "D5", the vehicle will respond to a throttleincrease by the operator to provide forward motion. The solenoid valve27 will produce an output pressure in accordance with the curves shownin FIGS. 3 and 5. FIG. 3 depicts the pressure output of the solenoids 27and 28 for fifty (50%) percent throttle by virtue of line 171 and forone-hundred (100%) percent throttle by line 173. FIG. 3 also depictscurves, or lines, which define the engine speed range for the ratiosselected in the transmission. With reference to lines 172 in FIG. 3 theengine speed will decrease when an upshift occurs. To accomplish theengine decrease, the on-coming clutch--e.g.: clutch "C2" during aone/two shift, must absorb the engine inertia. To accommodate this, theclutch timing is controlled by the trim boost pressure reflected in thetrim chamber 74 of the appropriate accumulator 50. The curves shown inFIG. 4 represent values similar to those in FIG. 3 during downshifts.The curves shown here, however, represent closed throttle andone-hundred (100%) percent throttle positions.

As best seen in FIG. 5, the solenoid valve 27 is controlled to provide apressure increase, during upshifting, before the solenoid valve 28. Thisfunction is provided in a well-known manner by the digital computerwhich provides the control function of the vehicle in response tovarious input signals or data as previously described. When the pressurelevel of solenoid valve 27 increased, the governor shuttle valve 115assumes the position shown in FIGS. 1 and 2. The governor shuttle valve115 will not be shifted from this position, during forward operation, aslong as the solenoid valves 27 and 28 do not malfunction. The outputpressure of the valve 27 is directed to the governor passage 67, to acton the shift valves 47, and to the primary chamber 154 in theaccumulator trim boost valve 30, to establish the output pressure levelof the regulator valve portion 157 and the boost pressure at eachaccumulator 50, as communicated through trim passage 77. As seen inFIGS. 3 and 5, this creates a step function for the governor pressurewhile the accumulator trim boost pressure cycles between high and lowvalues.

The pressure output level of the solenoid valve 28 lags that of valve27, but achieves the same levels. The pressure output of the valve 28 isdirected to the secondary boost chamber 155. When the pressure of valve28 is equal to the pressure of valve 27, the trim boost pressure will beat a minimum as established by the biasing action of the spring 160 andthe reduction in the projected area of the boost plug 151 resulting fromthe cross sectional area of pin 158. This permits the use of a singletrim boost control valve 30 for all of the accumulators 50. Because theshift valves 47A through 47D are cascaded, the trim boost pressure onthe respective accumulators 50A through 50D is effective only during theshift sequence controlled by the upshifting valve. To eliminate the pin158 from the trim boost pressure determination, equal diameter pinextensions can be incorporated on both sides of the plug 151 with onepin end passing into the valve bore 165 and the other pin end disposedin a bore in the bottom of chamber 154 and being connected to exhaust.

As the vehicle speed increases, the pressure in passage 67 will increasein accordance with the schedule-depicted in FIG. 3. At a predeterminedspeed, depending on throttle position, the output pressure of valve 27will be increased to effect upshifting of the shift valve 47A--therebycausing the clutch "C2" to be pressurized and the clutch "C1" to beexhausted through the valve 48A to return line 90A. The plug 151 isforced against the spring 160 to established an appropriate pressure,depending on vehicle parameters, within the chamber 74B of theaccumulator 50B to control the pressure rise schedule of the clutch"C2". The remaining chambers 74 will also be pressurized but theaccumulators 50 connected therewith are inoperative at that stage. Thepressure output of the valve 28 will then be increased to cause the plug151 to be pressure balanced and the output pressure of the regulatorvalve portion 157 to reduce to the minimum value.

A further increase in the vehicle speed, at a constant throttle setting,will result in increased pressure in the passage 67 at the desired shiftspeed as shown by the curves in FIGS. 3 and 5. At a predeterminedpressure, the shift valve 47B will be upshifted and the trim boostpressure in the passage 77 will be increased such that the accumulator50C will be effective to control the engagement pressure schedule at theclutch "C3" while the clutch "C2" is exhausted through the valve 48B tothe return line 90B. FIG. 5 shows the output pressure of solenoid valve27 at line portion 174, is at a pressure level greater than the outputpressure of solenoid valve 28 at the line portion 175. This establishesthe trim boost pressure in passage 77 that is available in the chamber74C during the two/three ratio interchange. When the shift is completedand the output pressure of solenoid valve 28 is increased to a levelequal to the outlet pressure of solenoid valve 27, the trim boostpressure in passage 77 will decrease to a minimum value as determined bythe spring 160.

As the vehicle speed continues to increase, the valve 47C will reach theshift point to control the three/four ratio interchange through theengagement of clutch "C4", as controlled by the accumulator 50D, whilethe valve 48C controls the disengagement of the clutch "C3". The trimboost pressure will be controlled in the manner previously described.The four/five ratio interchange, resulting from an upshift at the valve47D, represented by the engagement of the clutch "C5", as controlled bythe accumulator 50E, and the disengagement of the clutch "C4" will occurin the manner as described above for the other ratio interchanges.

It should be apparent that the valve 30 is effective to control the trimpressure at each upshift ratio interchange. The combination of the plug151 and the solenoid valves 27 and 28 assist the valve 30 in providingthis feature. Closed throttle downshift ratio interchanges are madewithout trim boost inasmuch as engine torque is minimal during thisevent. The curves of FIG. 5 also show the hysteresis "H" between theupshift and the downshift schedule. For example, the one/two upshiftbegins at the point 177A on curve 97 while the two/one downshift beginsat the point 178A on curve 97. Likewise, the two/three upshift occurs atthe point 177B while the three/two downshift occurs at the point 178B.The other upshift and downshift points are evident on the curve 97.

The difference between the upshift and downshift points represents thehysteresis. This function (hysteresis) is provided to prevent "hunting"by the transmission control when the vehicle is operated close to anyshift point. While the hysteresis function can be provided in many ways,the most common is to provide a differential area on the shift valvewhich is subjected to the on-coming clutch pressure after the shift.With this structure, the forces holding the valve in the upshiftedposition are greater after the shift such that the control pressure inpassage 67 must be at a lower level when a downshift occurs.

The upshift schedules at fifty percent and one-hundred percent throttle,represented by governor pressure schedules and engine speed curves, areshown in FIG. 3. As will be apparent from reviewing the curves shown,the engine speed is higher during the ratio interchange and theinterchanges occur at higher engine speeds as the throttle setting isincreased. The downshift schedules of zero percent and one-hundredpercent throttle, represented by governor pressure schedules and enginespeed curve, are shown in FIG. 4. As is apparent from the curves, thedownshift vehicle speed increases as the throttle position is increased.These are conventional shift schedules.

The transmission can be limited to less than all of the forward speedratios by manipulation of the manual valve. For example, if the operatordoes not wish the transmission to reach the fifth forward speed ratio,the manual valve will be moved to the "D4" position. In this position,the "D4" passage 40 will be pressurized. The pressure in this passage 40is directed to the chamber 70D of the valve 47D. This pressure acts onthe land 57D to assist the spring 85D in resisting the upshifting of thevalve 47D. The pressure in the passage 67 will not be sufficient toforce the upshifting of the valve 47D.

Manipulation of the manual valve to the other forward ratio positionsrepresented by "D3" through "D1" will result in limiting the upshiftingof the transmission to the third forward through first forward ratiosrespectively. In "D3", the passage 41 and therefore chamber 70C will bepressurized to prevent the upshifting of the valve 47C such that thetransmission control cannot energize the clutches "C4" and "C5".Likewise, the pressurization of the passages 43 and 41 respectively toprevent the shifting of valves 47B and 47A, respectively. The operatorcan control the upshifting to some extent by starting in "D1" andupshifting to successive gears as desired. The upshift will occur if theother parameters are satisfied, that is the pressure in passage 67 issufficient to shift the respective valves. The operator can downshiftfrom any forward to a lower forward ratio through the manipulation ofthe manual valve 24.

The purpose of the shuttle valve 115 is to direct the higher pressureoutput of the two solenoid valves 27 and 28 to the lower end of the plug151 and to the governor passage 67. When the control system is operatingas intended, the solenoid valve 27 will, at a predetermined portion ofthe cycle, provide a higher pressure than the solenoid 28 during theupshift cycle. However, if the solenoid valve 28 should inadvertentlyproduce a higher pressure than the solenoid valve 27, the chamber 133will be at a higher pressure resulting in the shuttle valve 115 beingforced into the chamber 114. In this position, the passage 131 isconnected to the passage 147 between lands 140 and 141 and the passage117 is connected with the passage 148 between the lands 141 and 143.Thus, it should be evident that the output pressures of the solenoidvalves 27 and 28 and their function is then reversed.

If either solenoid valve 27 or 28 should malfunction and provide aconstant output pressure other than zero, the normal shift sequenceswill be interrupted. The operator can eliminate this situation bybringing the vehicle to a stop and shifting to reverse. When the reverseratio is selected, the passage 93 is pressurized. This results in theshuttle valve 91 being moved to direct the fluid pressure in passage 93to the clutch "C3". Also during a shift to reverse, the forward-reversecontrol 25 will condition the necessary mechanism (i.e.: a synchronizer)to the proper position.

The pressure in passage 93 will also act on the lands 120 and 101 toshift the spool valve members 118 and 100 against the respective springs127 and 108. When the spool valve members 118 and 100 are shifted, thechambers 126 and 107 are connected with the output pressures from thesolenoid valves 28 and 27, respectively. If one of these solenoid valveshas malfunctioned in a high output pressure condition, the respectiveinterlock valve 94 or 95 will remain in the shifted position because ofthe pressure bias in the respective chamber 107 or 126. When theoperator shifts to a forward drive condition, only one solenoid valvepressure output will be available to the governor passage 67 and boostpassage 150. This will result in maximum trim boost pressure at theaccumulators 50 such that the operator will experience harsh shifting atall throttle conditions. This shift feel will continually remind theoperator that some repair is required. However the operator will havethe entire range of operation until the repairs are effected.

Also with this control, if either solenoid malfunctions to maintain alow output pressure, the operator will also feel harsh shifts but ashift from forward to reverse is not required to clear the system. Ifthe shuttle valve 51 should become stuck in either extreme condition,the transmission will undergo harsh shifting, again alerting theoperator to the need for repair. If the shuttle valve 51 malfunctions inthe center position, all the transmission shifts will be soft,suggesting slipping clutches, which will alert the operator to the needfor repair. Malfunctions in the valve 30 will result in harsh shiftingwhen continual high trim boost pressure is present and in soft shiftingif continual low trim boost pressure is present. As explained above,these conditions alert the operator to the need for repair.

The foregoing description of the exemplary embodiment of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Obvious modifications or variations are possiblein light of the above teachings. The embodiment was chosen and describedto provide the best illustration of the principles of the invention andits practical application to thereby enable one of ordinary skill in theart to utilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. All suchmodifications and variations are within the scope of the invention asdetermined by the appended claims when interpreted in accordance withthe breadth to which they are fairly, legally and equitably entitled.

I claim:
 1. A transmission shift signal control comprising:regulatorvalve means for providing a trim pressure fluid for a plurality ofaccumulators including a boost plug; shuttle valve means for selectivelydirecting pressurized fluid to first and second ends of the boost plugand for directing pressurized fluid to a governor passage; firstinterlock valve means for selectively directing pressurized fluid from afirst solenoid valve means to said shuttle valve means to be therebydirected to the first end of the boost plug and said governor passage;second interlock valve means for selectively directing pressurized fluidfrom a second solenoid valve means to said shuttle valve means to bethereby directed to the second end of the boost plug when thepressurized fluid from said first solenoid valve means is at a levelgreater than the pressurized fluid from said second solenoid valvemeans; and, said boost plug being responsive to the fluid from the firstand second interlock valve means to switch the fluid from the secondinterlock valve means to the first end of the boost plug when thepressure level of the fluid directed from the second interlock isgreater than the fluid directed from the first interlock.
 2. Atransmission shift signal control comprising:manual valve means fordirecting fluid to establish forward and reverse drive ratios; regulatorvalve means for providing a trim pressure fluid for a plurality ofaccumulators including a boost plug; shuttle valve means for selectivelydirecting pressurized fluid to first and second ends of the boost plugand for directing pressurized fluid to a governor passage; firstinterlock valve means for selectively directing pressurized fluid from afirst solenoid valve means to said shuttle valve means to be therebydirected to the first end of the boost plug and said governor passageand including first interlock chamber means; second interlock valvemeans for selectively directing pressurized fluid from a second solenoidvalve means to said shuttle valve means to be thereby directed to thesecond end of the boost plug when the pressurized fluid from said firstsolenoid valve means is at a level greater than the pressurized fluidfrom said second solenoid valve means and including second interlockchamber means; and, said boost plug being responsive to the fluid fromthe first and second interlock valve means to switch the fluid from thesecond interlock valve means to the first end of the boost plug when thepressure level of the fluid directed from the second interlock isgreater than the fluid directed from the first interlock, both saidfirst and second interlock chamber means being connected with the fluidfrom said first and second solenoid valve means respectively when thereverse drive ratio is selected by the manual valve means.
 3. Atransmission control comprising:a source of fluid pressure including apump means and a system regulator valve; a plurality of fluid operatedselectively engageable torque transmitting means for establishing aplurality of speed ratios in a transmission, respective ones of saidtorque transmitting means being interchanged during a change of ratios;a plurality of shift valve means for controlling the interchange ofratios each including accumulator means for assisting in controllinginterchange time, each accumulator means having a trim chamber means forproviding a reaction pressure during said interchanges; trim boostsupply means for supplying and controlling a trim boost pressuredelivered to the trim chamber means including pressure regulator meansfor supplying pressurized fluid and boost plug means having a firstchamber means for increasing the fluid pressure at the pressureregulator means and a second chamber means for counteracting the firstchamber means; and, solenoid valve means in combination with a pair ofinterlock valve means and a shuttle valve means for selectivelysupplying and directing pressure to the first chamber means when eachratio interchange is initiated and to the second chamber means prior tothe occurrence of a subsequent ratio interchange.